Russia has been accused of conducting a “nefarious” month-long submarine operation over British subsea infrastructure including pipelines and internet cables.

According to defence secretary John Healey, the operation involved three Russian vessels – two Gugi spy submarines and an Akula class submarine – that did not damage any key infrastructure. 

Russia initially deployed an attack submarine entering international waters in the High North, which includes the European Arctic and the surrounding areas of the North Atlantic. But military personnel believed the vessel was being used as a distraction, and after working with allies including Norway identified other Russian vessels above some subsea infrastructure.

The Royal Navy then deployed a Type 23 frigate HMS St Albans, RFA Tidespring and Merlin helicopters to track the attack submarine as it operated near British territorial waters.

Subsea fibre optic cables act as a major backbone for global digital communications, relaying over 99% of international data traffic, including voice calls and internet data. But they are notoriously difficult to defend as they stretch out for thousands of kilometres in some of the remotest parts of the world’s oceans.

The military operation ultimately saw British ships cover thousands of miles, while the RAF and the Navy deployed sonobuoys to track the Russian vessels.

The Ministry of Defence said that although the Russian attack submarines have now headed back towards their homeland, the UK has kept both naval vessels and aircraft ready to respond should they return.

“I want to pay tribute to the UK personnel who spent many days tracking these Russian submarines in extremely challenging and treacherous conditions,” Healey said. “While the eyes of many – understandably – were on the Middle East, our British Armed Forces were simultaneously responding to rising Russian threats north of the UK.

“As we act to defend our interests and allies in the Middle East, we are tackling increasing threats to Nato in the High North, maintaining strong support for Ukraine and protecting our UK homeland.

“To Putin, I say this: we see you, we see your activity over our underwater infrastructure. You should know that any attempt to damage it will not be tolerated and would have serious consequences.”

Over the last two years, the UK has seen a 30% increase in Russian vessels threatening UK waters. The Royal Navy recently completed 10 days of intensive monitoring operations of Russian warships and a submarine that entered UK waters in the English Channel and North Sea. 

In November, Amazon Web Services unveiled plans to build a new 5,000km subsea data cable to connect Maryland, US, with County Cork in Ireland.